The invention concerns an illumination system for a microscope as defined in the preamble of claim 1.
The illumination system for a microscope contains, in the illumination beam path, a light source, a collector lens, an adjustable aperture diaphragm, and a condenser lens. When objectives with different degrees of magnification are used, a Kxc3x6hler illumination system must cover a wide range of apertures and fields. In the case of a microscope, the illumination system must ensure that both a 100xc3x97/0.90 objective with a large aperture and a small object field, and a 4xc3x97/0.10 objective with a small aperture and large object field, can be used.
Known illumination systems make available an excess of light, only a small portion of which is used. The light sources used for illumination systems of this kind are high-output halogen lamps with a large lamp filament, which generate a large geometric light flux. The geometric light flux results from the large illumination surface and the wide emission angle (beam angle) of the halogen lamp.
Only a portion of the large geometric light flux can be used by the various objectives, however. What is used is either a large object field (a large illuminated area) with a small aperture (narrow beam angle), or a small object field (a small illuminated area) with a large aperture (wide beam angle).
The use of high-output halogen lamps of course also causes thermal problems in the microscope stand. The stand expands because of the heating. In addition to the undesired thermal radiation, this can also cause a preset focus to be lost because of the expansion.
WO 94 07 166 A1 discloses. an illumination system for a microscope in which an optimized geometric light flux is ensured by the use of replaceable condenser heads and condenser lenses. Selectable installation of the optical subassemblies makes it possible to illuminate both small fields with large apertures and large fields with small apertures. This illumination system has proven successful. The replaceable optical subassemblies associated with this illumination system require a high level of manufacturing complexity, however. In addition, the condenser lens must also be replaced whenever an objective is changed.
DE 196 44 662 discloses an illumination system for a microscope in which no optical components are moved. A light source that shines through a planar LCD is provided for illumination. A selectable transparent/opaque pattern is generated on the LCD by way of a control system. By changing the size of the pattern, the illumination can be adapted to different apertures. With this device, different illumination conditions are established under software control. Here again, however, it is necessary for the light source to make available a large geometric light flux, only a small portion of which is used.
DE 31 08 389 A1 discloses an illumination system for a microscope in which a controllable liquid crystal cell having a defined structure is used as a mechanical stop. Differently configured liquid crystal cells are used for each of the various types of illumination, for example incident/transmitted light illumination, oblique illumination, dark-field illumination, phase-contrast illumination, and polarized illumination.
Because of the permanently defined electrode structures of the respective cells, they can be used only for defined magnification conditions in the microscope. If the magnification is changed by using a different microscope objective, a different liquid crystal cell adapted thereto must be installed in the microscope. This is, of course, also the case whenever a different type of microscope illumination is selected.
DE 37 34 691 C2 discloses an illumination apparatus for a microscope in which a plurality of LEDs, combined into a two-dimensional matrix, are provided as the light source. This compartmentalized LED matrix contains a plurality of individual LEDs, in the colors red, green, and blue (RGB), arranged next to one another. By way of a corresponding control system, individual LEDs can be activated and a corresponding illumination pattern can thus be generated. It is of course very complex and expensive to provide and control so many LEDs.
DE 42 31 406 A1 discloses a bright-field transmitted-light illumination system for microscopes in which a transparent disk having a centrally arranged screen pattern is provided in the illumination beam path. With this illumination system, uniform illumination of the field diaphragm is achieved because the screen pattern creates multiple images, arranged next to one another, of the lamp filament of the light source.
DE 37 08 647 C2 describes a Kxc3x6hler illumination arrangement for microscopes having a collector lens, an aperture diaphragm, and a condenser lens. With this illumination system, uniform illumination of the object plane is achieved by the fact that a diffusing element is arranged between the collector lens and a reflector adjacent to the light source. The. collector lens projects an image of the light source at infinity.
It is generally true of all light sources of planar configuration, that the light source makes available a high geometric light flux, only a small portion of which is used.
It is therefore the object of the present invention to minimize the thermal load on the microscope and the specimen.
This object is achieved, according to the present invention, by the features recited in the characterizing portion of claim 1. Further advantageous developments are the subject matter of the dependent claims.
The combined arrangement of the two light sources in the illumination beam path results in an illumination that, with a fixed condenser, achieves an optimized geometric light flux for high-magnification objectives with a large aperture and small object field, and for low-magnification objectives with a small aperture and large object field.
Arranging the second light source in a central bore of the collector lens makes available a simple mount for the light source.
In an embodiment of the invention, diffusing components in the form of a diffusion disk and/or a frosted lens surface can be provided in the illumination beam path.
LEDs are advantageously used as the light source. Other point light sources, such as small halogen lamps or incandescent lamps, can of course also be used. The LEDs have the advantage of creating almost no heat when operating, and of emitting the light in directed fashion. When white-light LEDs are used, their brightness can also be regulated, without a color shift, by way of a simple change in current. With the use of RGB LEDs,. which also generate white light and can be dimmed by changing the current, it is moreover possible to control the intensity of each individual color separately.
The illumination system having the two light sources is preferably arranged in a separate housing and is configured as a retrofittable component for existing microscope condenser heads. The illumination system can of course also be permanently joined to the condenser lens, thus forming a single component.
In a further embodiment of the invention, .an electrical control system is provided with which the two light sources can be switched separately or together. The brightness and/or color temperature of the light sources can thereby be correspondingly regulated. The control system furthermore has a voltage supply for the light sources in the form of a battery or rechargeable battery and/or a DC line power supply.
In a further embodiment of the invention, provision is made for the RGB LEDs to be activated sequentially in order to generate an RGB television signal. A black-and-white video camera or a corresponding chip can be used in this context as the light-sensitive receiver module. Provision is also made for the LEDs to be activated in pulsed mode to generate flashed illumination.